Abstract: Marc Imhoff (see links below for references) apparently was the first scholar to note the striking correspondence between the light pattern and the spatial distribution of urban areas. His interests in developing a spatial view of the global distribution of sprawl led him to work with the city lights map. He noted that the light pattern overestimates urbaninzation, when taking a more careful look at a larger-than-global scale, and worked with a research team from Goddard Space Center to study, with greater accuracy, the noted correspondence (http://earthobservatory.nasa.gov/Study/Lights/lights_3.html ):
"The researchers classified the lights left on the image, after [a] dimming process, as urban area. The previously lit areas on the image that shrank back were classified as peri-urban (low-density suburban areas or farmland). Any areas that had no lights to begin with were labeled as non-urban. They compared these classifications to the boundaries on the actual urban areas of the city and found there was a close match. Imhoff and his team now had a set of numbers (threshold values), which told them to what extent the lights from any portion of the United States should be dimmed to get an accurate and spatially explicit representation of urbanization."
To look at the world's population, in a broad view only, consider using the data in the files of the Digital Chart of the World (DCW). The data is general, but is designed for viewing broad global pattern. Thus, Figure 2 shows a sequence of static images representing the world's urbanized areas and populated places. DCW categorizes both urbanized area and populated places in a hierarchy according to size, represented as 1, 2, and 3, from highest to lowest, in the maps below. There are also a few other categories noted in the legends below (Figure 2a-2j--scroll across to see the entire sequence). The urbanized areas are colored in tones of yellow from lightest at the high end to darkest at the low end; the populated places are colored in tones of khaki, from lightest at the high end to darkest at the low end. In addition, there is an overall continuum of shading from lightest yellow to darkest khaki across all the categories.